1. Field of the Invention
This invention relates to electronic musical instruments and more particularly to circuits which produce chorus or ensemble effects therein.
2. Description of the Prior Art
Chorus or ensemble tonal effects have long been recognized as very desirable in the production of music. The reason for this is that a chorus effect adds a richness, warmth and depth to music.
The effect is created by generating, in unison, a number of similar tone signals which are slightly out of tune or phase relationship.
Thus, in the production of music by an orchestra, the effect is generated naturally by numbers of similar instruments, such as violins for example, playing in unison. Since many musicians are unable to play exactly in tune, the chorus effect is created without any special effort or instrumentation.
Many circuits have been devised for generating a chorus effect in electronic musical instruments. The majority of these use vibrato effects applied to a number of equally pitched tone signals. The modulated tone signals are then sounded simultaneously. The resulting sound has an ensemble characteristic which is similar to a true chorus effect. By increasing the vibrato vibrations, more realistic chorus effects can be generated.
U.S. Pat. No. 2,905,040 shows an apparatus for producing a chorus effect wherein two audio frequency oscillators at equal nominal musical pitches are driven by two out of phase vibrato signals. The resulting vibrato modulated audio signals are then recombined electrically to produce a chorus effect. In addition, this patent discloses an electro-mechanical apparatus for producing a chorus effect wherein a delay line is continuously scanned by means of two commutators which are driven in synchronism, but 180.degree. out of phase, at a vibrato rate. The delay line is driven by a source of electrical musical tone signals. The resultant vibrato modulated tone signals are then reproduced and recombined acoustically.
U.S. Pat. No. 3,083,606 shows two vibrato units which are driven by out of phase control voltages and which modulate the tone signals emanating from a single tone signal source. The outputs of the vibrato units are amplified and reproduced acoustically to produce an ensemble effect.
U.S. Pat. No. 3,749,837 shows a circuit for producing an ensemble effect wherein shift registers are used to frequency modulate the audio signal.
U.S. Pat. No. 3,833,752 shows a system wherein three parallel shift registers are used and which are driven by out of phase vibrato oscillators to generate an ensemble effect.
U.S. Pat. No. 3,866,505 shows a system which is substantially equivalent to that of U.S. Pat. No. 3,833,752.